Variable attenuator calibrator



Oct. 12, 1954 s, B 2,691,760

VARIABLE ATTENUATOR CALIBRATOR Filed March 5, 1946 CRYSTAL CURRENTINDICATOR 3 SOURCE INVENTOR. THEODORE S. SAAD ATTORNEY Patented Oct. 12,1954 A UNITED STATES PATENT OFFICE VARIABLE ATTENUATOR CALIBRATORTheodore S. Saad, West Roxhury, Mass, assig'nor,

by mesn'e assignments, to the United States of America as represented bythe Secretary of the Navy Application March 5, 1946, Serial No. 652,195

4 Claims. ,1

This invention pertains to calibrators for wave guide variableattenuators, and more particula'rly to such calibrators designed andconstructed so as to retain their own calibration essentially constantwith time, and so as to render them stable and efiective over wideranges of operation.

Attenuator calibrators hitherto known in the art were undesirable inthat either they were fragile and so did not retain constant their owncalibration, or were unstable for a complete calibration over widerange. I

An object of this invention is to provide a c'alibrator for calibratingvariable atteunators at microwave frequencies.

Another object of this invention is to provide a calibrator forcalibrating variable attenuators at microwave frequencies which willaccurately retain'its calibration.

Still another object of this invention is to provide a calibrator of theclass described which is of rugged construction and which is simple touse.

Further objects and advantages of this invention will be apparent fromthe claims and description, taken in connection with the drawings inwhich:

Fig. 1 is a diagram showing (a) relative position of all the componentparts of a system for operating the invention herein described, and (b)detailed arrangement of the several parts of the calibrator alone; and

Fig. 2 is a plan view of the critical component of the calibrator,showing position of the openings in a broad face of the wave guidesection, upon which openings the operation of this invention isdependent.

Referring to Fig. 1 there is shown a short wave guide section It havingopenings I I and I2 in one broad face, said openings leading into othershort wave guide sections I3 and I4, fixedly secured to section It. Bothends of wave guide section It and the open ends of sections I3 and I 4have flanges I5, It, I! and I8 respectively to form conventional chokejoints for electrical continuity when opposed by appropriate faces.Openings I I and I2 are separated from each other by an odd multiple ofquarter wave lengths in order to cancel reflections which they wouldotherwise introduce. Openings II and 20 are both down from the line byan appreciable amount, at least 20 db being recommended. In other words,the power passing out through either opening is defined approximately bythe following relation: 20:10 logm of ratio amounts that diiferslightly, oneor two db being suitable in many cases. The absolute valueof 2 this difference may be any fixed value within suitable limits, butthat value must be known accurately. Fig. 1 also shows a short waveguide section 59 with choke joint flanges 20 and El and a fixedattenuator 22 fixedly secured, and a crystal 23 with a crystal holder 28 fixedly secured to its own choke joint flange 25. Fixed pad attenuator22 is to prevent resonance effects, and is on the order of 5 to 10 db. Acrystal current indicator 2% is shown schematically in Fig. 1. Waveguide section I9 is readily movable with respeot to wave guide sectionIt, and in operation alternately opposes choke joint flanges I? and I8.The assembly comprising short wave guide section I9, crystal 23, crystalholder 24 and crystal current indicator 2t will hereinafter be referredto as a padded crystal holder.

In operation energy from a source passes down a wave guide, reaching theattenuatorunder calibration, the calibrator herein described, and amatched load, in that order. Fig. 1 illustrates this arrangement. Theattenuator is first set on zero. Assume that opening I2 is down 20 dbfrom the line, and that opening I I is down 21 from the line. The paddedcrystal holder is placed first over opening Ii and the crystal currentis observed. The padded crystal holder is then placed over opening l2and the attenuator is stopped down until the new crystal current dropsto the value previously observed. The reading on the attenuator scaleshould now be observed and recorded, and it will be noted that theadvance in attenuator setting resulted in an attenuation increase of 1db.

The next step is to place the padded crystal holder again over openingII and observe the crystal current now present. As before, the paddedcrystal holder then is placed over opening I2, and the attenuator isadvanced further to make the current indication equal the oneimmediately preceding. The new reading on the attenuator scale isobserved and recorded, it being noted that the advance in attenuatorsetting has resulted in an attenuator increase of 1 db from 1 dbto 2 db.

It is apparent that continuation of this stepby-step process will resultin data which may be tabulated as suggested in the followinghypothetical example:

Total Atten- This calibration information may be presented appropriatelyand conveniently in the form of a calibration curve.

What is claimed is:

1. Apparatus for calibrating variable microwave attenuators comprising,a source of microwave electromagnetic energy, a matching load, a waveguide section for coupling said load to said source through theattenuator to be calibrated, said wave guide section having a pair ofopenings differing in size therein and spaced by an odd multiple of aquarter wave length of the energy from said source and adapted to coupleenergy from said wave guide section with a constant, predetermined,known difference of attenuation, and means to provide an indicationproportional to the amount of energy coupled from said wave guidesection through each of said openings.

2. Apparatus for calibrating variable microwave attenuators, comprisinga source of microwave electromagnetic energy, a matching load, arectangular wave guide section for coupling said load to said sourcethrough the attenuator to be calibrated, said wave guide section havinga pair of openings in the broad side thereof spaced by an odd multipleof a quarter wave length of the energy from said source and difiering insize to couple energy from said wave guide section with a constantpredetermined, known difference of attenuation, and an indicator formeasuring the amount of energy coupled from said wave guide sectionthrough each of said openings.

3. Apparatus for calibrating variable microwave attenuators comprising,a source of microwave energy, a matched load, a rectangular wave guidesection for coupling said lead to said source through the attenuator tobe calibrated, said wave guide section having in the broad side thereofa pair of openings differing in size to couple energy from said waveguide section at two constant, differing, known values of attenuation,said openings being spaced axially in said wall by an odd multiple of aquarter wave length of the energy of said source to prevent reflectionof energy from said opening, and an indicator for measuring the amountof energy drawn from said wave guide section through each of saidopenings.

4. Apparatus for calibrating a variable microwave attenuator, comprisinga source of microwave energy, a matching load, a rectangular wave guidesection for coupling said load to said source through the attenuator tobe calibrated, said wave guide section having two branches coupled tothe broad side thereof through a pair of openings differing in size tocouple energy from said wave guide section at two constant differingknown values of attenuation, said openings being spaced axially alongsaid Wall by an odd multiple of a quarter wave length of the energy ofsaid source to prevent reflection of energy from said branches, and anindicator for measuring the amount of energy drawn from said wave guidesection through each of said branches.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,419,208 Frantz et a1 Apr. 22, 1947 2,422,601 Tashjian June1'7, 1947 2,444,060 Ohl June 29, 1948 2,522,563 Blitz Sept. 19, 1950

